This invention relates to a starter for an internal combustion engine of an automobile, and in particular to an improved starter having a planetary-type reduction gear.
FIG. 1 illustrates an example of the type of starter to which the present invention relates, the example shown in the figure being one disclosed in Japanese Laid Open Utility Model Application No. 58-132170. Since the starter is basically symmetrical about a centerline, only one half of the starter is illustrated. The starter has a direct current (DC) motor comprising a stator having magnetic poles 1, a cylindrical yoke 2 surround the stator and by which the poles 1 are supported, and a rotor within the stator having a rotor core 3, a rotor shaft 4, and rotor windings 5. The right end of the rotor shaft 4 is connected to an output shaft 6 through a planetary reduction gear. The output shaft 6 is rotatably supported at the end distant from the rotor shaft 4 by a front bracket 7 through a journal bearing 8, while the other end of the output shaft 6 is rotatably supported by a middle bracket 9 through a journal bearing 10, the middle bracket 9 being rigidly secured to the yoke 2. At the end adjoining the rotor shaft 4, the output shaft 6 has a hollow portion 6a on the outside of which is formed a flange 6b. One end of the rotor shaft 4 is rotatably supported by a journal bearing 11 provided on the inner surface of the hollow portion 6a and is separated from the output shaft 6 in the longitudinal direction by a steel ball 12. The flange 6b of the output shaft 6 has a number of support pins 13 secured thereto at intervals along its circumference, and each support pin 13 rotatably supports a planet gear 15 through a journal bearing 14 which fits over the support pin 13. Each of the planet gears 15 meshes with a sun gear 4a formed on the outer surface of the rotor shaft 4 and with a ring gear 2a formed on the inner surface of the yoke 2. The sun gear 4a, the ring gear 2a, and the planet gears 15 constitute the planetary reduction gear which drivingly connects the rotor shaft 4 with the output shaft 6.
An overrunning clutch 16 is mounted on the output shaft 6 and is connected thereto by a helical spline 6c formed on the outer surface of the output shaft 6. The outer race 17 of the overrunning clutch 16 is slidably mounted on the spline 6c so as to rotate therewith while being able to move in the axial direction of the output shaft 6. The inner race 18 of the clutch 16 is rotatably mounted on the output shaft 6 through a journal bearing 22, which enables it to move axially along the output shaft 6 together with the outer race 17 and at the same time enables it to rotate with respect to the output shaft 6. A pinion 18a which engages with an unillustrated engine starter ring is formed on the outer circumferential surface of the inner race 18 at the end which is remote from the motor. The inner race 18 and outer race 17 have rollers 19 disposed therebetween which allow rotational force to be unidirectionally transmitted form the outer race 17 to the inner race 18. The rollers 19 are prevented from moving in the axial direction by an end plate 20 and a cover 21. A stopper 23 for limiting the axial movement of the overrunning clutch 16 is secured to the output shaft 6 by a ring 24. A lever 25 for moving the overrunning clutch 16 along the output shaft 6 in the axial direction thereof has a forked portion at its inner end which fits around the outer race 18 so that the outer race 18 can rotate inside the forked portion. The outer end of the lever 25 is rotatably connected to the plunger 27 of an electromagnetic switch 26. The middle portion of the lever 25 is pivoted on a spring-mounted fulcrum 28.
The operation of the illustrated apparatus is as follows. When the electromagnetic switch 26 is turned on, the plunger 27 of the switch 26 is pulled inwards (to the left in FIG. 1), and the lever 25 is rotated counterclockwise about the fulcrum 28. The inner end of the lever 25 which fits around the overrunning clutch 16 is swung to the right, causing the overrunning clutch 16 to slide to the right along the helical spline 6c of the output shaft 6 until the pinion 18a meshes with the unillustrated starter ring of an engine. When the motor is operated, the rotation of the rotor shaft 4 is reduced in speed and transmitted to the output shaft 6 by the planetary reduction gear. The rotation of the output shaft 6 is transmitted to the starter ring via the pinion 18a of the overrunning clutch 16, thereby cranking the engine. When the engine has started and come up to speed, the inner race 18 of the overrunning clutch 16 begins to rotate faster than the output shaft 6 and therefore freewheels with respect to the outer race 17. At this time, the electromagnetic switch 26 is turned off, and the plunger 27 moves outwards to the right, the lever 25 pivots in the clockwise direction about the fulcrum 28, the pinion 18a of the inner race 18 disengages from the starter ring of the engine, and the overrunning clutch 16 returns to its initial position.